An auger filling apparatus which uses mechanical revolution has been conventionally employed for filling a powder toner for electrophotograph.
An external additive is usually adhered to the surface of the toner used for electrophotograph for higher fluidity. There have been many occasions where the external additive adhered to the toner surface falls off with the conventional auger apparatus to cause a quality problem. This issue has become more serious since a toner with smaller particle diameter has been used recently compared to conventional equivalents in order to obtain a high-quality image.
Regarding a toner material, an external additive and an antistatic additive comprising silica and titanium are adhered on the surface of the toner particle to maintain the fluidity and the electrostatic property of the toner. Application of strong stress on the toner exfoliates the additives, which causes negative effects on the electrostatic property during an image forming process.
For example, Japanese Patent Application Laid-Open (JP-A) No. 2002-249101 discloses an auger-type powder filling apparatus, which is suitable for mass production with a few items. As mentioned above, this powder filling apparatus has a problem that the apparatus stresses the toner and that the external additive falls off from the surface of the toner particles. Moreover, the apparatus is of large size, requiring a spacious installation site and industrial 200 V power supply.
Japanese Patent (JP-B) No. 3549053 proposes a powder filling apparatus, which fluidizes a powder by injecting a gas. In this proposal, a powder is transferred to a powder container and filled while the tip of a transfer nozzle for transferring and discharging a powder fluidized by a gas in the powder repository is surrounded by the powder residing in the powder repository. This filling apparatus applies less stress to the toner compared to the auger-type apparatus. However, the container must be pressurized due to the characteristics of the apparatus and sealed since the force does not transmit unless the pressure inside the toner repository is 6 kPa or greater, which results in a time lag of about five seconds. In addition, there is a problem that additional charges of the toner cannot be made since the repository is sealed. Moreover, there is a problem that the powder dust of toner easily disperses.
JP-A No. H04-226672 (Japanese Patent Application Publication (JP-B) No. H06-14960) describes a transfer by means of a bellows pump, i.e. an accordion pump. It is possible to transfer a liquid by means of the transfer method of this patent literature. However, a powder toner gets plugged in the bellows in transferring the powder toner; therefore, it cannot be transferred. Although weirs and chokes in bellows or flow paths do not usually affect the transfer of a liquid, there is a problem that the transfer of a powder toner is difficult since the powder toner accumulates at weirs and chokes in bellows or flow paths.
JP-A No. 2005-67651 proposes a transferring method by fluidizing a powder toner by supplying a gas. However, the powder transfer of the present proposal is not efficient, and sufficient accuracy in the transferred quantity cannot be achieved.
In JP-A No. 2002-302169, a toner is transferred by a so-called mono pump, but this does not resolve the problem of the external stress on the toner.
Regarding the filling efficiency, there are contradicting issues that higher filling accuracy requires longer filling time and that the shorter filling time decreases the filling accuracy. In particular, when the filled quantity is less than the displayed sales quantity, low filling accuracy causes not only a drawback for a customer but also a possible trust problem of the company who has sold goods with less than labeled quantity. On the other hand, a toner with more than a specified quantity is beneficial to a customer, but the accumulated excess may put pressure on the profit of the company.
Therefore, high filling accuracy as well as short filling time as filling efficiency is always required. As a specific solution to resolve this problem, JP-A No. 2005-67652 proposes a method to complete promptly the filling by degassing, i.e. removing air from the filled toner. However, this proposal has a problem that the weight cannot be accurately measured because the toner is sucked around the degassing mechanism when the filling and degassing are performed simultaneously.
Also, JP-A No. 2005-75372 proposes a method of filling a toner in a container with a limited volume in a short period of time with high density. Herein, the toner container is topped with a hopper, and the toner container and the hopper are connected. The predetermined amount of the toner is overflowed in the connected container, and the hopper is detached when the filling is completed. However, with the method of this proposal, it takes long to stabilize the scale on which the toner is weighed since the hopper is bulky and tall. Moreover, there is a problem that the toner adhered to the inside of the hopper flows out when the hopper is detached upon the completion of filling, which smudges around the toner container and the peripheral equipments.
Also, a method to increase the toner filling accuracy and further to reduce the filling time is proposed, wherein the lower end of a toner discharge pipe is made porous with a triple tube described in, for example, JP-A No 2005-41501; the discharge pipe is degassed through the backside of the porous portion; a toner is sucked to the surface of the porous portion to form ‘plugs’ to swiftly suspend the falling toner. However, this proposed method requires the formation of strong ‘plugs’ since the transfer needs to be stopped quickly without sacrificing the transferring amount of toner within the toner discharge pipe. Also, in the case of an automatic filling machine that performs a continuous filling operation, these ‘plugs’ must be removed before the start of the filling in the next toner container. Therefore, an air pulse of about 0.3 MPa is supplied from the backside of the porous portion for cleaning. Because of this, the ‘plugs’ do not get blown into the toner container or the hopper, but there is a problem that a part of the toner blown off gets out of the container to become the source of powder dust.